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35 lines
835 B
Idris
35 lines
835 B
Idris
data Fin : Nat -> Type where
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FZ : Fin (S k)
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FS : Fin k -> Fin (S k)
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natToFin : Nat -> (n : Nat) -> Maybe (Fin n)
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natToFin Z (S j) = Just FZ
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natToFin (S k) (S j)
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= case natToFin k j of
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Just k' => Just (FS k')
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Nothing => Nothing
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natToFin _ _ = Nothing
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integerToFin : Integer -> (n : Nat) -> Maybe (Fin n)
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integerToFin x Z = Nothing
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integerToFin x n = if x >= 0 then natToFin (fromInteger x) n else Nothing
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data IsJust : Maybe a -> Type where
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ItIsJust : IsJust (Just x)
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-- Testing that %allow_overloads lets this one through!
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partial
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fromInteger : {k : Nat} ->
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(n : Integer) ->
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{auto prf : IsJust (integerToFin n k)} ->
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Fin k
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fromInteger {k} n {prf}
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= case integerToFin n k of
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Just val => val
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foo : Fin 5
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foo = 3
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bar : Fin 5
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bar = 8
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